It is well known that radon, a radioactive gas formed by the radioactive decay of radium, actinium, or thorium, poses a significant health hazard to humans if they are exposed to radon gas in quantity. Recently, it has been discovered that radon gas seeps into homes and other structures from radioactive element sources found in the earth. Once in the home, the radon attaches to air-borne particles which may be inhaled. Continual exposure to radon over four picoCuries per liter of ambient air breathed is believed to significantly increase the incidence of lung cancer.
It is well known that adequate ventilation of lower floors of structures alleviates the harmful radon concentrations. Thus, most homes with unsafe radon concentrations may be made livable merely with adequate ventilation.
Currently, there are four ways in which to detect and determine radon concentrations. All of these methods are derived from alpha particle detection methods which are: the scintillation counter, the gas counter including both Geiger and proportional types, the solid state junction counter, and the activated charcoal detector.
The scintillation counter wa historically the first utilized in early experiments on radioactivity. The scintillator was viewed with a microscope to count the individual flashes of light produced by each alpha particle stopping event. In the modern scintillation type counter, the scintillation material is disposed on a photocathode of a photomultiplier tube which amplifies the signal and provides information about the energy of the alpha particle. An analyzer is then required for analysis of the analog signal from the multiplier to count the alpha particles present. The coating of the scintillator must be opaque to prevent the admission of ambient light into the system. To accomplish this, the coating must be very thin making it susceptible to scratches which lead to "light leaks". The use of a scintillator for radon detection has heretofore been described by Madnick et al, U.S. Pat. No. 4,984,535 issued Jan. 16, 1990. The Madnick device, as described, would be expensive to manufacture, would be susceptible to "light leaks", and would require calibration.
Gas-filled alpha particle detectors use a specific gas as the detector material depending upon whether the mode of operation is a Geiger counter or an ionization/proportional counter. In either case, the working gas for alpha or radon detection is hermetically sealed. Entrance to the ionization zone by the incoming alpha particle is through a thin, fragile plastic or metal window. The output signal pulse is constant in the Geiger counter operation but is related to the energy of the alpha particle in the ionization and proportional counter operations. The existence of delicate windows for the entrance apertures for the incoming alpha particles make the ga filled counters unsatisfactory for continual use because the window may be easily damaged.
The junction counter is a solid state p-n junction with a reverse bias which collects ionization charges from passage of an alpha particle through the depletion layer. It can be made compact and portable. The limitation of the junction counter lies in the stringent requirements for avoiding scratching and abrasion of the metallic electrode surface of the detector. This electrode is light sensitive and the coating serves to block ambient light; thus it can be easily scratched resulting in a "light leak". Equally important, the active surface must be free from moisture and dust.
Another means for detection of radon concentrations is the activated charcoal detector. This method, however, is not adaptable for continual monitoring of radon concentrations in real time.
From this it is evident that the radon detection methods, currently available, have intrinsic deficiencies which make them impractical to monitor ambient radon concentrations in real time. The present invention, however, remedies these deficiencies by providing a rugged radon detector that monitors ambient radon concentrations in real time. Further, the present invention needs no calibration means to distinguish between alpha particles, beta particles or gamma rays as the present invention is only capable of monitoring alpha particle disintegrations from radon as well as from other radioactive sources.